DE69836462T2 - SECONDARY BATTERY - Google Patents

Description

AREA OF TECHNOLOGY

The The present invention relates to a secondary battery with a non-aqueous Electrolytes and in particular a positive electrode thereof.

TECHNICAL BACKGROUND

In lately has been developing wearable and cordless types of electronic devices like audio and video devices and personal computers made rapid progress, and it persists a strong demand for a secondary battery of small size, low Weight and high energy density as a driving source of energy Equipment. In particular, there are high expectations that a lithium secondary battery with a negative electrode, in which metallic lithium is active Material used is a battery that is able to a high voltage and a high energy density are available too put. Because of insufficient Safety and reliability But is such a lithium battery practically not used Service.

It It is believed that safety is diminished because the negative Metallic lithium electrode by repeated charging and Discharging into a dendritic form passes over what is possible internal short circuits and a heat generating reaction between the electrolyte and the lithium in dendritic Shape leads.

To solve the problem, a lithium ion secondary battery having a negative electrode made of carbon material capable of reversibly intercalating and deintercalating lithium, and a lithium-containing transition metal oxide positive electrode such as LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ been proposed.

There Lithium charging into the carbon material of the negative electrode intercalated and theoretically on the negative electrode plate never causes a deposition of lithium, consists in Such a lithium ion secondary battery has the advantage that internal short circuits confined in the cell are superior and the battery in safety and reliability is.

Even in such a lithium ion secondary battery having a negative Electrode of carbon material capable of lithium reversibly to intercalate and deintercalate, but becomes lithium gradually deposited on the negative electrode plate while the Loading and unloading take place repeatedly, and the problem has existed that at the last stage of cycle life safety and security reliability the battery was reduced.

It is therefore an object of the invention to solve the problem and to provide a cell or battery, which in the Charging and discharging cycle life characteristics, safety and security Superior reliability is by depositing lithium on a negative electrode plate is prevented in the last stage of the cycle life.

A invention secondary battery includes a positive electrode comprising an active material and a has conductive material, a negative electrode and a Electrolytes in contact with the positive and negative electrode, wherein the conductive material Ketjenblack and flake graphite, characterized that the content of Ketjenblack, based on 100 parts by weight of active material, ranging from about 0.2 parts by weight to about 1.0 parts by weight and the value of [3X + (3/8) Y] is in the range of is about 1.0 to about 3.5, wherein X is the content of Ketjenblack in Units of parts by weight and Y the content of flake graphite in units of parts by weight per 100 parts by weight of active Material is.

in the above structure it is desirable that the electrolyte is a non-aqueous Electrolyte is.

in the above structure it is desirable that the positive electrode is band-shaped.

in the above structure it is desirable that the positive electrode is band-shaped, the negative electrode is band-shaped and the positive and negative electrodes with a separator in between placed against each other and spiral be wound up.

the According to the above construction, the positive electrode has an increased capacity for the Electrolytes, the electrolyte is uniform throughout the electrode distributed, a metallic material forming the active material is prevented from doing so on the surface of the negative electrode To be separated, and as a result, the cycle life extended with repeated loading and unloading.

If furthermore Ketjenblack and flake graphite both as conductive Material used in addition to the above effect the positive electrode improved in its resistance.

SHORT DESCRIPTION THE DRAWING

1 is a vertical section through a cylindrical cell according to an embodiment of the invention.

BEST WAY, THE INVENTION OUT

When Index for the physical property of a Russian like Ketjenblack becomes used the absorption of dibutyl phthalate oil (DBP oil absorption). Ketjenblack is a type of soot powder and a trademark of Ketjen Black International Company. It is believed that the DBP oil absorption in relation to receptivity for one Electrolyte is. If a soot with high DBP absorption than one conductive material for the positive electrode is used increases the capacity for the electrolyte, the distribution of the electrolyte in the width direction of the electrode is guaranteed and as a result, the performance with respect to repeated loading and unloading Discharge cycles increased. The DBP oil absorption from Ketjenblack EC is about 360 ml / 100 g, that of Ketjenblack EC600JD is 500 ml / 100 g, and that of acetylene black is 120 ml / 100 g.

The means that Ketjenblack superior EC in cycle performance is because it is in an amount of about 1/3 of that of acetylene black a generally similar one receptivity for the Electrolyte supplies. When watching a cell in the last stage the charge and discharge cycle life had a cell with Ketjenblack no clogging of the separator at the two ends of an electrode plate in the width direction and no elimination of lithium in the Center up and showed superior Safety and reliability.

On the other hand In a cell with acetylene black, the cycle performance was not the same greatly increased like in a cell with Ketjenblack, even if the capacity of the increased positive electrode was made by a larger Added amount of acetylene black has been. It is believed that this is because in the case of Acetylene black the higher order chain structure due to the mechanical Load during of the mixing process in making the mass for the positive Electrode destroyed and reduces the capacity becomes.

One Russ like Ketjenblack and acetylene black has different physical Values and structures, and it is believed that the DBP oil absorption as well as other, different properties an impact on the absorption capacity for one Have electrolytes. In other words, it is believed that the Cycle performance by optimizing the different properties a Russ is improved and a sufficiently large capacity for the positive Ensured electrode by using such a soot becomes. So far, Ketjenblack was the only soot that had a significant increase reached the cycle performance.

• 1) die Struktur einer hohlen Schale mit an der Aussenseite angesammelten Graphitkristallen besitzt, die eine dünne Schicht bilden;
• 2) erwünschterweise eine DBP-Ölabsorption von etwa 200 ml/100 g, stärker erwünscht von 350 ml/100 g oder darüber zur Verfügung stellt; und
• 3) eine Oberfläche (Stickstoffadsorptionsverfahren) von etwa 500 m²/g oder darüber besitzt, stärker erwünscht von etwa 1000 m²/g oder darüber. Weitere Eigenschaften von Ketjenblack sind hierunter aufgeführt.
• 4) Eine Iodadsorption von 950 mg/g (etwa 500 mg/g oder darüber).
• 5) Flüchtige Komponenten von 1 %.
• 6) Ein pH-Wert von 9,5.
• 7) Eine Porosität von 69,3 % (etwa 35 % oder darüber).
• 8) Flüchtige Komponenten von 0,5 %.
• 9) Ein scheinbares spezifisches Gewicht von 150 g/liter.

It is desirable that the Ketjenblack used is characterized in that it

• 1) has the structure of a hollow shell with graphite crystals accumulated on the outside forming a thin layer;
• 2) desirably provides a DBP oil absorption of about 200 ml / 100 g, more desirably 350 ml / 100 g or above; and
• 3) has a surface area (nitrogen adsorption process) of about 500 m ² / g or above, more desirably about 1000 m ² / g or above. Other properties of Ketjenblack are listed below.
• 4) An iodine adsorption of 950 mg / g (about 500 mg / g or above).
• 5) Volatile components of 1%.
• 6) A pH of 9.5.
• 7) Porosity of 69.3% (about 35% or above).
• 8) Volatile components of 0.5%.
• 9) An apparent specific gravity of 150 g / liter.

If according to of the present invention, a mixture of Ketjenblack and flake graphite is used is the amount of added Ketjenblack about 0.2 to 1.0 parts by weight per 100 parts by weight of active material of the positive electrode, and the value of [3X + (3/8) Y] is 1.0 or above and at 3.5 or below, where X is the content of Ketjenblack in Units of parts by weight and Y the content of flake graphite in units of parts by weight.

According to the above contents, the amount of Ketjenblack added is controlled so that the density of the positive electrode active material in the mass (hereinafter referred to simply as the positive electrode active material density) is about 3.0 to 3.5 g / cm ³ , when an active material having a true density of about 5 g / cm ^{3 is used} for the positive electrode.

When Ketjenblack mixed flake graphite can be natural graphite, more synthetic Graphite and the like, and it is with respect to electronic conductivity he wishes, that the flake graphite has a particle size of about 0.1 microns to about 50 μm and in particular of about 3 microns to about 10 microns has.

The particle size of Ketjenblack is not specifically limited.

Now become embodiments the invention as well as embodiments, which do not form part of the present invention, among them described with reference to the drawings.

Exemplary embodiment 1 (not forming part of the present invention)

In 1 Fig. 3 shows a vertical section through a cylindrical cell according to the embodiment. In 1 is a provided with a safety valve sealing plate 2 with an interposed insulating seal 3 in the opening of a cell case 1 made by processing a stainless steel sheet which is resistant to an organic electrolyte. A positive electrode 4 and a negative electrode 5 be with a separator in between 6 wound spirally several times and in the housing 1 accommodated. A positive leader 7 extends from the positive electrode 4 and is with the sealing plate 2 connected. A negative leader 8th extends from the negative electrode 5 and is with the bottom of the cell case 1 connected. In the upper and lower part of the plate group 10 are insulating rings 9 appropriate. The positive electrode 4 and the negative electrode 5 will be described in detail below.

LiCoO ₂ as a positive electrode active material 4 was synthesized by mixing Li ₂ CO ₃ and Co ₃ O ₄ and heating at 900 ° C for 10 hours. Ketjenblack powder (manufactured by Ketjen Black International under the trade name of Ketjenblack EC) was added to 0.2 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1.0 parts by weight, 1.2 parts by weight and 1.5 parts by weight 100 parts by weight of the LiCoO ₂ powder is added and mixed therewith and emulsified in an aqueous carboxymethylcellulose solution in conjunction with 7 parts by weight of a fluororesin binder to prepare pastes of the respective positive electrode materials. The pastes were coated on both sides on a 0.03 mm thick aluminum foil as a metal plate, dried and rolled, and corresponding positive electrode plates of 0.18 mm thick, 51 mm wide and 420 mm long were prepared. The obtained positive electrode plates were dried at 250 ° C. In this way became a positive electrode 4 made with the metal plate and a positive material applied on both sides of the metal plate.

For the negative electrode 5 a synthetic graphite KS44 made by Timcal Company was used. To 100 parts by weight of the synthetic graphite, three parts by weight of styrene-butadiene rubber was added and mixed therewith and emulsified in an aqueous carboxymethylcellulose solution to prepare a paste. The paste was coated on both sides on a 0.02 mm thick copper foil, dried and rolled, and a negative electrode plate of 0.18 mm thick, 53 mm wide and 450 mm long was prepared.

Then an aluminum ladder became 7 attached to the positive electrode plate, and a nickel conductor 8th was attached to the negative electrode plate. The thus prepared positive and negative electrode plates were spirally wound with a polypropylene separator of 0.025 mm thick, 59 mm wide and 1200 mm long therebetween, and housed in a cylindrical cell case of 18.0 mm in diameter and 65 mm in height. The electrolyte was a solvent prepared by mixing of ethylene carbonate (EC), diethylene carbonate (DEC) and methyl propionate (MP) in a volume ratio of 30: 50: 20, with 1 mol / liter of LiPF ₆ dissolved therein. The electrolyte was filled in the cell case, then the opening of the cell case with the sealing plate 2 locked. In this way, a cell A was prepared.

Exemplary embodiment 2

Powders of LiCoO ₂ prepared in a manner similar to that of Embodiment 1, Ketjenblack powder, flake graphite (Product No. KS10, manufactured by Timcal Company) and a fluororesin binder were emulsified in an aqueous carboxymethylcellulose solution, and pastes of various compositions were prepared. The contents of Ketjenblack were 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.8 parts by weight and 1.0 parts by weight, respectively, per 100 parts by weight of LiCoO ₂ . The contents of flake graphite were 0.5 part by weight, 1.0 part by weight, 2.0 parts by weight, 3.0 parts by weight and 4.0 parts by weight per 100 parts by weight of LiCoO ₂ . The contents of fluororesin binder were 7 parts by weight. The paste was applied to both sides of an aluminum foil of 0.03 mm in thickness, dried and rolled to prepare a positive electrode plate of 0.18 mm in thickness, 51 mm in width and 420 mm in length. The other structure was similar to that of Embodiment 1. In this way, a cell B was prepared.

Exemplary embodiment 3 (not forming part of the present invention)

Powders of LiCoO ₂ prepared in a manner similar to that of Embodiment 1, Ketjenblack, acetylene black (manufactured by Denki Kagaku Kogyo KK) and a fluororesin binder were emulsified in an aqueous carboxymethylcellulose solution, and pastes of various compositions were prepared. The contents of Ketjenblack were 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.5 parts by weight, 0.8 parts by weight and 1.0 parts by weight, respectively, per 100 parts by weight of LiCoO ₂ . The contents of acetylene black were 0.3 part by weight, 0.5 part by weight, 1.0 part by weight, 1.5 parts by weight and 2.0 parts by weight per 100 parts by weight of LiCoO ₂ . The contents of fluororesin binder were 7 parts by weight. The pastes were applied to both sides of an aluminum foil 0.03 mm thick, dried and rolled to produce positive electrode plates 0.18 mm thick, 51 mm wide and 420 mm long. The other structure was similar to that of Embodiment 1. In this way, a cell C was prepared.

Comparative example

100 parts by weight of the LiCoO ₂ powders prepared in a manner similar to that of the embodiment, three parts by weight of acetylene black and seven parts by weight of a fluororesin binder were emulsified in an aqueous carboxymethylcellulose solution to prepare a paste. The paste was applied on both sides to an aluminum foil of 0.03 mm in thickness, then dried and further rolled to prepare a positive electrode plate of 0.18 mm in thickness, 51 mm in width and 420 mm in length. The other structure was similar to that of Embodiment 1. In this way, a cell D was prepared.

When next was at five Specimens of each of the cells used in the compositions described above were measured, the impedance (1 kHz AC) measured, and thereafter, a charge and discharge cycle life test was performed. in the Charging and discharging cycle life test have been charging and discharging cycles at 20 ° C repeated under the conditions given below. For the store became constant voltage / constant current charging at a charging voltage of 4.2V, a current limited to 800mA and a charging time carried out for 2 hours, and Konstantstromentladung was for a discharge with a Discharge current of 1200 mV and a discharge voltage of 3.0 V performed. Then, with the working capacity of the tenth cycle, it was set as an initial capacity, that the last stage of the cycle life was reached, when the initial capacity in half had fallen off. The densities of the active materials of the positive Electrodes, the initial capacities, the impedances and a result of the cycle life test become shown in Tables 1, 2 and 3.

(Table 1)

(Table 2)

(Table 3)

In Table 1 was the cycling performance of cell A according to no part of the present invention Invention forming embodiment increased compared to cell D of the comparative example. It is desirable, the content of Ketjenblack ranges from about 0.3 to about 1.2 parts by weight. When the content of Ketjenblack is 0.2 parts by weight or less, the positive electrode collecting property is reduced, and the impedance of the cell increases yourself. When the content of Ketjenblack is 1.5 parts by weight or more is, will the density of the positive electrode active material in the Mass of the positive electrode decreases, and the capacity of the cell decreased to 1150 mAh or below.

In Table 2, the cycle performance of the cell B according to the embodiment of the invention was increased as compared with the cell D of the comparative example. When the content of Ketjenblack is 0.1 part by weight or less, the cycle performance is not significantly increased, the positive electrode collecting property is reduced, and the cell impedance increases. The impedance of the cell was high when the value of [3X + (3/8) Y] was less than 1, where X is the content of Ketjenblack in units of parts by weight and Y is the content of flake graphite in units of parts by weight while the density of the positive electrode active material was reduced and the capacity of the cell was 1150 mAh or less when the value was over 3.5 was. Thus, a cell having a high initial capacity, a low impedance and a superior cycling performance was obtained when the content of Ketjenblack was in a range of about 0.2 parts by weight to about 1.0 parts by weight per 100 parts by weight of the active material, and Value of [3X + (3/8) Y] was in a range of about 1.0 to about 3.5, wherein X is the content of Ketjenblack in units of parts by weight and Y is the content of flake graphite in units of parts by weight.

In Table 3 was the cycling performance of cell C according to no part of the present invention Invention forming embodiment increased compared to cell D of the comparative example. If the content of Ketjenblack was 0.1 part by weight or less, the cycle performance was not significantly increased, the collection property of positive electrode was reduced, and the cell impedance was higher. The impedance of the cell was high when the value of [3X + Z] was below 1.1, where X is the content of Ketjenblack in units of parts by weight and Z is the content of acetylene black in units of parts by weight is while reduces the density of the positive electrode active material was and the capacity the cell was 1150 mAh or less when the value was over 3.5 was. Thus, a cell that has a high initial capacity, a low impedance and a superior Cycle performance, obtained when the content of Ketjenblack in a range of about 0.2 to about 1.0 parts by weight and the value of [3X + Z] ranges from about 1.0 to about 3.5 where X is the content of Ketjenblack in units of parts by weight and Z is the content of acetylene black in units of parts by weight is.

When The flake graphite blended with Ketjenblack can be more natural Graphite, synthetic graphite and the like.

Although LiCoO _{2 was used} as a positive electrode active material in the embodiment, lithium-containing transition metal chalcogenides such as LiNiO ₂ and LiMn ₂ O ₄ may be used alternately, and a similar effect to that described above may be obtained in such a case.

INDUSTRIAL APPLICABILITY

A Battery, which is a superior initial capacity and a superior one Performance of repeated charge and discharge cycles and high safety even at the last stage of the life of the repeated charging and discharging cycles can be obtained.

1

cell case

2

sealing

3

insulating poetry

4

positive electrode

5

negative electrode

6

separator

7

positive electrode conductor

8th

negative electrode conductor

9

insulating ring

10

disk array

Claims (6)

A secondary battery comprising: a positive electrode having active material and a conductive material comprising Ketjenblack and flake graphite; a negative electrode and an electrolyte in contact with the positive and negative electrodes, characterized in that the Ketjenblack has the structure of a hollow shell with graphite crystals accumulated on the outside, a dibutyl phthalate oil absorption of at least 200 ml / 100 g and a surface area of 500 m ² / g or more, the content of Ketjenblack is within a range of 0.2 parts by weight to 1.0 part by weight per 100 parts by weight of the active material and the value of [3X + (3/8) Y] is in the range of 1.0 to 3.5, wherein X is the content of Ketjenblack in units of parts by weight and Y is the content of flake graphite in units of parts by weight per 100 parts by weight of active material. secondary battery according to claim 1, characterized in that the electrolyte a non-aqueous electrolyte is. secondary battery according to claim 1, characterized in that powder of Ketjenblacks and powder of the active material mixed and by a binder be connected to each other. secondary battery according to claim 1, characterized in that the positive Electrode a metal plate and a positive electrode material which is present on both sides of the metal plate, and the positive electrode material, the conductive material and the active Includes material that is mixed together. secondary battery according to claim 1, characterized in that the positive electrode band-like is, the negative electrode is band-shaped and the positive and negative electrode with a separator between them laid and spiraled be wound up. Secondary battery according to claim 1, characterized in that the active material is at least one selected from the group of LiCoO ₂ , LiMn ₂ O ₄ and LiNiO ₂ material.